Department of Neurology, University of Massachusetts Medical School, Worcester, MA 01605, USA.
Department of Neurology, University of Massachusetts Medical School, Worcester, MA 01605, USA.
Neurobiol Aging. 2021 Sep;105:327-332. doi: 10.1016/j.neurobiolaging.2021.04.030. Epub 2021 May 8.
GGGGCC (GC) repeat expansion in the first intron of C9ORF72 is the most common genetic cause of amyotrophic lateral sclerosis and frontotemporal dementia, two devastating age-dependent neurodegenerative disorders. Both sense and antisense repeat RNAs can be translated into 5 different dipeptide repeat proteins, such as poly(GR), which is toxic in various cellular and animal models. However, it remains unknown how poly(GR) is synthesized in patient neurons. Using a reporter construct containing 70 GC repeats flanked by human intronic and exonic sequences, we show that translation of the poly(GR) frame does not depend on repeats or the CUG start codon in the poly(GA) frame, suggesting poly(GR) is not produced after ribosomal frameshifting in the poly(GA) frame. However, deletion analysis suggests that translation of the poly(GR) frame depends on the length of the intronic sequence 5' adjacent to GC repeats. Moreover, several 5´ cis elements that are predicted to be involved in alternative splicing regulates poly(GR) synthesis. These results suggest that translation of repeat RNAs in the poly(GR) frame is regulated by multiple cis elements, likely through RNA secondary structures and/or associated RNA binding proteins.
GGGCC (GC) 重复扩展在 C9ORF72 的第一个内含子中是肌萎缩侧索硬化症和额颞叶痴呆的最常见遗传原因，这两种疾病都是破坏性的、与年龄相关的神经退行性疾病。正义和反义重复 RNA 都可以翻译成 5 种不同的二肽重复蛋白，如 poly(GR)，它在各种细胞和动物模型中都是有毒的。然而，目前尚不清楚多聚（GR）在患者神经元中是如何合成的。使用含有 70 个 GC 重复序列的报告基因构建体，侧翼为人内含子和外显子序列，我们表明，多聚（GR）框的翻译不依赖于重复序列或多聚（GA）框中的 CUG 起始密码子，这表明多聚（GR）不是在多聚（GA）框中的核糖体移码后产生的。然而，缺失分析表明，多聚（GR）框的翻译依赖于 GC 重复序列 5' 相邻内含子序列的长度。此外，几个预测参与可变剪接的 5'顺式元件调节 poly(GR)的合成。这些结果表明，重复 RNA 在 poly(GR)框中的翻译受多个顺式元件调控，可能通过 RNA 二级结构和/或相关的 RNA 结合蛋白。
